/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.jena.sparql.lang;

import java.util.*;

import org.apache.jena.query.ARQ;
import org.apache.jena.query.Query;
import org.apache.jena.query.QueryParseException;
import org.apache.jena.query.Syntax;
import org.apache.jena.sparql.core.Var;
import org.apache.jena.sparql.core.VarExprList;
import org.apache.jena.sparql.expr.Expr;
import org.apache.jena.sparql.syntax.*;

/** Calculate in-scope variables from the AST */
public class SyntaxVarScope {
    /* SPARQL 1.1 "in scope" rules These define the variables from a pattern that are
     * in-scope These are not the usage rules.
     * 
     * Syntax Form In-scope variables
     * 
     * Basic Graph Pattern (BGP) v occurs in the BGP Path v occurs in the path Group
     * { P1 P2 ... } v is in-scope if in-scope in one or more of P1, P2, ... GRAPH
     * term { P } v is term or v is in-scope in P { P1 } UNION { P2 } v is in-scope
     * in P1 or in-scope in P2 OPTIONAL {P} v is in-scope in P SERVICE term {P} v is
     * term or v is in-scope in P (expr AS v) for BIND, SELECT and GROUP BY v is
     * in-scope SELECT ..v .. { P } v is in-scope if v is mentioned as a project
     * variable SELECT * { P } v is in-scope in P VALUES var (values) v is in-scope
     * if v is in varlist VALUES varlist (values) v is in-scope if v is in varlist */

    // Weakness : EXISTS inside FILTERs?

    public static void check(Query query) {
        if ( query.getQueryPattern() == null )
            // DESCRIBE may not have a pattern
            return;
        check(query.getQueryPattern());
        // Check this level.
        checkQueryScope(query);
        // Other checks.
        Collection<Var> vars = varsOfQuery(query);
        check(query, vars);
    }

    public static void check(Element queryPattern) {
        checkSubQuery(queryPattern);
        checkPatternAssign(queryPattern);
    }

    // Check assignment forms that require a new variable.  
    // BIND and FIND
    private static void checkPatternAssign(Element queryPattern) {
        VarScopeChecker v = new VarScopeChecker();
        ElementWalker.walk(queryPattern, v);
    }

    // Check sub-query by finding sub-queries and recursively checking.
    // Includes applying all checks to nested sub-queries.
    private static void checkSubQuery(Element el) {
        ElementVisitor v = new SubQueryScopeChecker();
        ElementWalker.walk(el, v);
    }

    // Check one level of query - SELECT expressions
    private static void checkQueryScope(Query query) {
        Collection<Var> vars = varsOfQuery(query);
        checkExprListAssignment(vars, query.getProject());
    }

    // get all vars of a query
    private static Collection<Var> varsOfQuery(Query query) {
        Collection<Var> vars = PatternVars.vars(query.getQueryPattern());
        if ( query.hasValues() )
            vars.addAll(query.getValuesVariables());
        return vars;
    }

    // Other check (not scoping at this level) of a query
    private static void check(Query query, Collection<Var> vars) {
        // Check any expressions are assigned to fresh variables.
        checkExprListAssignment(vars, query.getProject());

        // Check for SELECT * GROUP BY
        // Legal in ARQ, not in SPARQL 1.1
        if ( !Syntax.syntaxARQ.equals(query.getSyntax()) ) {
            if ( query.isQueryResultStar() && query.hasGroupBy() )
                throw new QueryParseException("SELECT * not legal with GROUP BY", -1, -1);
        }

        // Check any variable in an expression is in scope (if GROUP BY)
        checkExprVarUse(query);

        // Check GROUP BY AS
        // ENABLE
        if ( false && query.hasGroupBy() ) {
            VarExprList exprList2 = query.getGroupBy();
            checkExprListAssignment(vars, exprList2);
            // CHECK
        }
    }

    private static void checkExprListAssignment(Collection<Var> vars, VarExprList exprList) {
        Set<Var> vars2 = new LinkedHashSet<>(vars);
        exprList.forEachExpr((v, e) -> {
            Set<Var> varInExpr = e.getVarsMentioned();
            // Include mentioned variables
            // These may be unused in the query (in vars) but still contribute.
            vars2.addAll(varInExpr);
            checkExpr(vars2, e, v);
            vars2.add(v);
        });
    }

    private static void checkExprVarUse(Query query) {
        if ( query.hasGroupBy() ) {
            VarExprList groupKey = query.getGroupBy();

            // Copy - we need to add variables
            // SELECT (count(*) AS ?C) (?C+1 as ?D)
            List<Var> inScopeVars = new ArrayList<>(groupKey.getVars());
            VarExprList exprList = query.getProject();

            for ( Var v : exprList.getVars() ) {
                // In scope?
                Expr e = exprList.getExpr(v);
                if ( e == null ) {
                    if ( !inScopeVars.contains(v) ) {
                        throw new QueryParseException("Non-group key variable in SELECT: " + v, -1, -1);
                    }
                } else {
                    Set<Var> eVars = e.getVarsMentioned();
                    for ( Var v2 : eVars ) {
                        if ( !inScopeVars.contains(v2) ) {
                            throw new QueryParseException("Non-group key variable in SELECT: " + v2 + " in expression " + e, -1, -1);
                        }
                    }
                }
                inScopeVars.add(v);
            }
        }
    }

    private static void checkExpr(Collection<Var> scope, Expr expr, Var var) {
        // Project SELECT ?x
        if ( expr == null )
            return;
        // expr not null
        if ( scope.contains(var) ) 
            throw new QueryParseException("Variable used when already in-scope: "+var+" in "+fmtAssignment(expr, var), -1 , -1) ;

        // test for impossible variables - bound() is a bit odd.
        if ( false ) {
            Set<Var> vars = expr.getVarsMentioned();
            for ( Var v : vars ) {
                if ( !scope.contains(v) )
                    throw new QueryParseException("Variable used in expression is not in-scope: " + v + " in " + expr, -1, -1);
            }
        }
    }

    private static String fmtExprList(VarExprList exprList) {
        StringBuilder sb = new StringBuilder();
        boolean first = true;
        for ( Var v : exprList.getVars() ) {
            Expr e = exprList.getExpr(v);
            if ( !first ) {
                sb.append(" ");
            }
            first = false;
            sb.append("(").append(e).append(" AS ").append(v).append(")");
        }
        return sb.toString();
    }

    private static String fmtAssignment(Expr expr, Var var) {
        return "(" + expr + " AS " + var + ")";
    }

    // Modified walked for variables.

    /** Visitor for subqueries scope rules . */
    private static class SubQueryScopeChecker extends ElementVisitorBase {
        @Override
        public void visit(ElementSubQuery el) {
            Query query = el.getQuery();
            checkQueryScope(query);
            // Recursively check sub-queries in sub-queries.
            check(el.getQuery());
        }
    }

    // Applies scope rules at each point it matters.
    // Does some recalculation in nested structures.

    public static class VarScopeChecker extends ElementVisitorBase {
        VarScopeChecker() {}

        @Override
        public void visit(ElementGroup el) {
            // BIND scope rules
            // (and service warning)

            for ( int i = 0 ; i < el.size() ; i++ ) {
                Element e = el.get(i);
                // Tests.
                if ( e instanceof ElementBind ) {
                    Collection<Var> accScope = calcScopeAll(el.getElements(), i);
                    check(accScope, (ElementBind)e);
                }

                if ( e instanceof ElementFind ) {
                    Collection<Var> accScope = calcScopeAll(el.getElements(), i);
                    check(accScope, (ElementFind)e);
                }

                if ( e instanceof ElementService ) {
                    Collection<Var> accScope = calcScopeAll(el.getElements(), i);
                    check(accScope, (ElementService)e);
                }
            }
        }

        private static Collection<Var> calcScopeAll(List<Element> elements, int idx) {
            return calcScope(elements, 0, idx);
        }

        /** Calculate scope, working forwards */
        private static Collection<Var> calcScope(List<Element> elements, int start, int finish) {
            Collection<Var> accScope = new HashSet<>();
            for ( int i = start ; i < finish ; i++ ) {
                Element e = elements.get(i);
                PatternVars.vars(accScope, e);
            }
            return accScope;
        }

        private static void check(Collection<Var> scope, ElementBind el) {
            Var var = el.getVar();
            if ( scope.contains(var) )
                throw new QueryParseException("BIND: Variable used when already in-scope: " + var + " in " + el, -1, -1);
            checkExpr(scope, el.getExpr(), var);
        }

        private static void check(Collection<Var> scope, ElementFind el) {
            Var var = el.getVar();
            if ( scope.contains(var) )
                throw new QueryParseException("FIND: Variable used when already in-scope: " + var + " in " + el, -1, -1);
        }

        private static void check(Collection<Var> scope, ElementService el) {
            if ( ARQ.isStrictMode() && el.getServiceNode().isVariable() ) {
                Var var = Var.alloc(el.getServiceNode());
                if ( !scope.contains(var) )
                    throw new QueryParseException("SERVICE: Variable not already in-scope: " + var + " in " + el, -1, -1);
            }
        }
    }
}
